


Disobedient

by Anonymous



Category: Dr. STONE (Anime), Dr. STONE (Manga)
Genre: Alternate Universe - Canon Divergence, Anal Fingering, Anal Sex, Bottom!Senku, M/M, Not Canon Compliant, Other Additional Tags to Be Added, Outdoor Sex, Phone Sex, Prostate Milking, Public Sex, Sexual Teasing, Teacher-Student Relationship, age gap, switching POVs, top!xeno
Language: English
Status: In-Progress
Published: 2020-09-13
Updated: 2020-09-13
Packaged: 2021-03-07 00:54:01
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 4,420
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26438257
Author URL: https://archiveofourown.org/
Summary: Senku stood next to his father, absolutely playing coy and shy, but Xeno was able to make out the smirk curling at the corner of his lips and the slight raise to his eyebrows.The little brat was proud of himself.
Relationships: Ishigami Senkuu/Dr. Xeno
Kudos: 50
Collections: Anonymous





	Disobedient

**Author's Note:**

> This was, originally, going to be a very, very, VERY long winded one shot.  
> Instead, it's going to be broken up into little chapters.  
> The tags above cover future chapters - please note I will most likely add more tags as the story progresses.

* * *

It had been a few days since Senku arrived at the NASA Johnson Space Center. 

His dad had been talking about the boy nonstop ever since his initial arrival at the branch. It wasn't uncommon - a parent so proud of their child to the point of over exaggerating their feats. Pinning drawings of round humanoid attempts at an actual human being to the fridge, or worse, taking them into work and covering their offices with them. The most pathetic attempt of bragging, of course, were the bumper-stickers for their overachieving children that so happened to get a few good grades. 

Which was exactly why Xeno would never pay any mind to Byakuya's ramblings about his prodigy of a son. His speeches were always the same as all the other proud parents. Xeno had absolutely no interest in what Byakuya would consider a genius child.

That was, until the boy finally came to visit. 

Xeno had never overheard the name of Byakuya's son. He only ever referred to him as that - His son. His _boy_ . He never once heard the name _Senku_ . That was - until Byakuya announced that his son would be moving to America until he finished his astronaut training. That his boy, _Senku_ , was ecstatic to be able to tour the NASA center. 

A mix of excitement and irritation grew within Xeno that day. 

The very boy that he had been helping for a while now. Filling his mind and his inboxes with messages of everything from physics and machinery to the lesser known discoveries of the cosmos. Senku had said _nothing_ of his approaching arrival. Obviously the boy was trying to keep it from him.

The memory of his first day visiting the NASA center was still vividly caught in Xeno's memory. Byakuya enthusiastically showing his son around the laboratories and offices, eventually making his way to Xeno's own desk. There was little emotion on his face as Byakuya introduced his son, his hand so proudly grasped onto Senku's shoulder as he spoke of the boy's interest in astronomy. According to Byakuya, Xeno would be a _great_ mentor for the boy. 

The man had _no idea_. 

Senku stood next to his father, absolutely playing coy and shy, but Xeno was able to make out the smirk curling at the corner of his lips and the slight raise to his eyebrows. 

The little brat was _proud_ of himself. 

Thankfully, they did not stay long. Byakuya had more to show the boy. But that did not stop Senku from turning his head around as they walked away, locking eyes with his _'new'_ mentor while giving a small wave to his hand. 

Xeno's eyes had only narrowed. Senku had caught him off guard, and he _knew_ it. And Xeno couldn't do a damned thing about it. 

Ever since Senku's first visit to the NASA center, he had been back nearly every day, constantly talking about his current studies and projects to any one that would lend him an ear. Most of the scientists watched the boy talk with wide eyes, not expecting such extreme knowledge to come from such a small mouth. For once, Byakuya was the parent that actually had the boy who made projects worth pinning all over his office walls. An actual child prodigy that shined so bright as he spoke of his rocket building and his attempts to get it through the earth's atmosphere that everyone around him would just nod along in total awe. 

His eager attitude and his desire to become an intern at the space center was the main reason he was allowed to keep coming back. Of course a few laboratories were no place for a young boy, he did not have the clearance to roam the entire center as he pleased. But as long as he did not bother the scientists too much, he was allowed to come in and wander or even help with a few mundane tasks. 

Xeno did not mind. Senku did not act like your usual child. He was not loud, or messy, nor did he throw temper tantrums when he did not get his way. Though, he usually seemed to get his way with most things, anyway. Byakuya did not seem to know how to scold the child at all. But, all things considered, it was rather pleasant to have the young genius around. His presence seemed to put more energy into many of the workers and scientists around the center - perhaps they felt a desire to impress the boy. 

No, Xeno did not mind at all. But it did make certain things... a _lot_ harder. 

He had never expected Senku to visit so early. They had been corresponding back and forth for a good while now, but the content of their interactions had... _changed_. Dramatically. And now, being in the same room as Senku's soft and young face, cheeks still round with baby fat... or being able to hear his mischievousness chuckle, or that snarky grin that appeared every time his father let Senku walk all over him... 

Xeno had found many excuses to excuse himself from the offices during the past few days. 

But, that day, it seemed that Senku was not going to let his mentor sneak off into the darkness without making things even _more_ difficult. 

Xeno was only leaving to refill his coffee mug, no longer desiring to hear Senku's grinning voice demand more money from his father. But slender arms had wrapped their way around Xeno's arm, tugging at his sleeve, a wide and toothy grin showing when Xeno looked down to the boy, his own eyebrow cocked high. 

"You're coming, right?" Senku asked, his smirk only growing, something about it seeming almost devilish. 

Xeno could only stare, entirely unsure of what he should be doing as the boy was gripping at his arm so earnestly. "I have no idea what you are talking about." 

A figure had come up behind the two of them, causing Xeno to turn his head to the side, watching as Byakuya invaded their small circle. Byakuya was always there. A reminder of the things that Xeno absolutely _could not_ do. 

"The company barbecue!" Byakuya said, his hands wide as his voice boomed. "I'm sure you got the email! Multiple ones, actually, we sent them all out a month ago! As well as a few reminders." 

"Ah, yes," right. Xeno nodded slowly, thinking back. "I had deleted them upon seeing them." As he always did with superfluous and time consuming company events. He had absolutely no desire to spend time with his coworkers outside of work. And especially not at some... barbecue event. 

But Byakuya only laughed at Xeno's words, "yeah, I figured you would have. I wasn't really going to bother asking you again, but," his eyes fell to Senku. 

Xeno did not follow Byakuya's line of sight. He already knew that Senku was looking back up at him with his wide and mischievous smile. This was not the first time that Senku had latched himself to Xeno, much to his own chagrin. It was easy to play off, at least. Xeno's placement in the company was exactly where Senku wanted to be someday, after all. So it was natural for the boy to have an attachment to the sort of man he wished to be. 

It had become a small joke around the work space. Senku being Xeno's _'assistant in training'_ with how often he chased the man around like a lost puppy. Even if it was only a jest, it was a proposition that would cause Senku's face to light up. Though, perhaps, not for the academic reasons that everyone else suspected. 

They did not know. 

Byakuya especially did not know. 

Not only just about the emails. That was nothing to be ashamed of. In fact, if they had only stayed emails, it would have become an amusing story. About how the boy that hacked into their systems not too long ago in search for help with his rocket, and how Xeno offered a helping hand to a mind clearly too bright to be wasted. 

But it advanced. Soon to texting - nearly constant. Senku coming to Xeno for more than just knowledge on the cosmos and how the rest of the world worked, but other things as well. Sometimes it was only to chat about his day. Sometimes it was bragging about a recent invention. Sometimes it was images of him or his friend. Sometimes, those images would have to be deleted as soon as Xeno saw them come in. Sometimes, it was help with... very personal things. 

Things that Senku most likely should have gone to his father for, but Xeno was more than willing to help. He had grown _too_ attached to the boy... 

Their time zones did not aid much in their conversations. Xeno often stayed up late into the morning hours to help Senku on nearly whatever he wished. It didn't matter what it was - if Senku required the aid, Xeno would be there. Maybe he was becoming a little _too much_ like Byakuya, in that regard... 

But, other times, Senku would often call Xeno during his working hours, the boy awake late at night, voice low and heavy with whines, always begging for Xeno to stay on the line just a while longer. Making Xeno quickly have to find a very, very private place to continue the call. 

Byakuya would never know that the reason behind his son becoming so fluent in English was due to their late night conversations... 

* * *

"You'll show me, right...?" 

"I've already told you where, Senku. I have even sent you diagrams and a _video_ to assist you, you cannot expect more out of me." 

Senku pouted - but he knew the man couldn't see it. Or, more-so, that he just wouldn't look over at the damn screen. 

Senku sat on his knees within the tall bathtub, arms draped over the side as he stared at his phone which sat perched up on the nearby stool with a couple of strategically placed towels. He could see Dr. X's face, but his mentor was not looking to his own propped-up phone at all. Instead, his focus was entirely on the computer in front of him, typing away at what was probably an important piece. 

A sigh left Senku as he sunk deeper into the hot water. He did not want to bother Dr. X _too_ much, but he had also agreed to this call in the first place! It was always so hard to get him to actually allow Senku to video call him... usually the guy always had some sort of excuse, but today seemed _perfect_ . Dr. X was alone at home, no one was around, and Dr. X had _finally_ agreed to face-time him...? There was _no way_ that Senku planned this bath for nothing! 

It didn't help that Dr. X had seemed to be in a down mood that evening, Senku was able to make out his furrowed brows as the computer screen held his focus. It only caused Senku to feel small, something minuscule when compared to his mentor's important work. He worked at NASA after all. And an important launch was coming up soon.

Maybe... a different night. Senku nodded slowly to himself in the bath. Perhaps after the rocket launch, when his mentor wasn't so busy. He could call during his own night time, when it would be the day for Dr. X, a weekend where he would have higher energy and less to worry about. 

"You've gone quiet." 

Senku looked up now, his gaze looking over the rim of the bathtub to see Dr. X glancing over to his phone, turning in his chair. Propping his chin onto the tub rim, Senku showed off a more pronounced pout. "You won't even look at me." He had even been working so hard on his English for this chat! And Dr. X wasn't giving him a single moment of his time.

The young boy watched as his mentor's eyes creased in his smile. "Oh?" Dr. X seemed more engaged now, "you've planned a show, have you?"

A quick huff quickly came from Senku, his hands pressing against the side of the bathtub, "No! Just...!" With a soft sigh, Senku's fingers began to tap against the porcelain rim, his gaze looking down at his hands "at least... walk me through it?" 

Senku did not look up to his phone, but he could hear Dr. X give a small hum. 

"All right. You'll need to put yourself on your knees." 

"I already am," Senku said softly, though he did shuffle slightly in the bath, now standing on them instead of sitting, his body now more visible to the man in front of him. "Now what?"

"I suppose this is easier with lube." 

"I'm in the water," Senku's head began to tilt, looking up now to meet his mentor's gaze through the phone camera, "doesn't that count?" 

"Hmm," Dr. X gave a small sigh, his hands crossing in front of his face. "It will do. But next time, do try and use some. You'll have an easier time."

A slow nod came from Senku, though it wasn't as if he just _had_ lube laying around the house. It wasn't exactly an easy thing to just go into a store and buy at his age - though he was sure he could come up with some scientific use for the stuff to warrant his purchase. "So...?" He questioned now, nerves only now picking up, intensified by his mentor's dark eyes looking so intensely at him through the phone camera. "What's next...?"

Dr. X took a moment, his eyes seeming to dance down Senku's body. "Your middle finger. Go slowly, now." 

Senku bit at his lower lip, brows knitted as he hesitantly pulled his dominant hand away from the bathtub rim. Just his middle finger - that's not a big deal. His fingers weren't even that big, and still super slender. Shuffling forward in the bathtub, he began to reach behind himself--

"Ah- No," Dr. X's quick words startled the boy, Senku's entire body feeling a cold chill. Did he already do something wrong?! "From the front. You'll have a much easier time curling your fingers."

With a small grumble, Senku shot a deep glare at Dr. X, bringing his hand back around. "Right, okay." He needed to rearrange himself, now sitting back on his heels as his hand slowly fell down deep beneath the water. His free arm braced his torso against the side of the tub, having to curl his body a bit to be able to reach far enough, the pad of his middle finger soon running against his hole. One finger - that was all his mentor had asked for. He could do that. The water would help. 

A shuddering breath left Senku's mouth as his middle finger slowly pressed into his body. The noise must have tipped Dr. X off, Senku able to hear a small ' _you're doing just fine_ ' from his phone. But he was not looking, his forehead pressed against his arm on the tub side, eyes closed, knowing that his face must have been a dark shade of red with how hot it felt. The fact... that his mentor was _watching_ it... 

It was not the first time they had video called, but it _was_ the first time Senku had touched himself in a place like _this_ while Dr. X watched.... 

"Are you moving your finger?" 

" _Yes_..." Senku breathed out, doing just that, his middle digit sliding in and out from his body in a slow and rhythmic pattern. 

"Good, now add a second. Use your ring finger." 

With a nod, Senku did as he was told, bringing a second finger into the mix. Immediately the sensation was different - a lot more uncomfortable at first, his body seeming to dislike the sudden intrusion. His brows knitted as his shoulders began to tense, but he did not back down from the task, doing his absolute best to press in both fingers as far as he could. 

"Ah," Dr. X's delight was clear in his voice, "are two fingers too much for you already? How tight you must be..." 

"Sh-shut up! Old pervert..." Senku knew his outburst would only amuse his mentor more - and he was right, soon hearing a chuckle come from the man. 

"Once you feel comfortable, begin to curl your fingers inward. As if you are trying to itch something." 

There _was_ no getting more comfortable, Senku felt. Even as he tried to slowly thrust the two fingers, it only felt weird. Once deep again, Senku did his best to imitate the motion Dr. X had described, both of his fingers now curling up within him. It... didn't feel _bad_ , but it didn't feel spectacular like everyone claimed it to be. "What... exactly am I looking for?"

"Hmm, something like... A small, round bulb," Dr. X began, his voice _too damn calm_ for all of this, "it will be a bit hard, though also soft." 

Senku only gave a scoff now, twisting his head to look at his phone, "you're not making any sense, but all right." 

Once more, Senku attempted to curl his fingers, and once more, Senku needed to look away from the phone. He was getting hard, but he was sure it wasn't due to some magical bundle of nerves in his body. Dr. X's gaze was on him, not leaving... It wasn't like Senku was really showing too much, everything beneath his shoulders being hidden by the tub. But that didn't seem to matter, his mentor wasn't even making a single sound, just watching with those damn eyes that sucked him in like a black hole. That thought alone was making Senku's cock twitch happily in the warm water, needing so bad to be touched. 

Senku focused his attention on his fingers, digging, curling, searching. But no matter what he did, or what angle he tried to twist his hand in, he could feel _nothing_. No lump, or 'bulb', nothing hard or soft. Just... tissue, wet tissue that wasn't even all that wet. Maybe Dr. X was right - water wasn't really anything compared to lube.

With a very rough sigh, Senku soon pulled his hand completely away from his body, both hands now braced against the rim of the tub, "this is stupid! I can't feel a damn thing - maybe I just don't have one." 

A laugh rang from Dr. X, "that's quite impossible." 

Senku slowly sunk into the bath, fully engulfed by the water now, only his head staying above the surface, and his phone only catching the tips of his hair. "I just feel dumb." 

"Don't become discouraged. Chances are, your fingers are still too small." 

A scoff rang from Senku, brows heavy as his face now lowered more into the water, his nose able to provide some air. He hated that - he absolutely _hated_ any time Dr. X treated him like a child. He wasn't a baby - he just had no experience in this! 

Though - his face softened, moving forward in the bath as his hands slowly climbed over the rim, followed by his grinning face. "What about _your_ fingers, sensei?" He purred it out, arms curling up on the side of the bathtub, his chin resting on them as his grin began to grow. "I think they would be _just_ long enough." 

There was a surge of pride that welled in Senku's chest as he watched his mentor's eyebrows slowly raise. Dr. X even gave a smirk - a look that caused Senku's heart rate to quicken. They were an entire ocean's distance apart from one another, there was no way Dr. X's fingers could _actually_ sink into him - but maybe his mentor had something else up his sleeve. 

"I think," Dr. X began, Senku's eyes lighting up at the way his mentor licked at his lips, his slender fingers reaching forward to hold his phone. Was this it? Would he finally show Senku something _good_ on camera...? 

"That's enough, for today."

Senku's grin left him then, face turning blank before twisting into pure distress, leaning forward as he grabbed at his own phone, "Wait - what?! Again!? No way, I had all of this planned!"

But Xeno only showed his usual kind smile, the chat screen soon turning off and showing Senku's home screen. Doing his absolute _best_ to not throw his phone, Senku slammed it back onto the stool of towels with a loud groan. He always did this! It wasn't the first time! Things got good, sometimes _amazing_ , and then someone would call, or he'd have a meeting! It was like he planned it, like it was his damn _kink_!

Senku laid himself back in the bath, absolutely fuming. How many times had he actually been able to get off with his mentor on the other end? Only a handful. And as for the latter, being able to hear Dr. X moan into the phone, well... that hadn't happened, _yet_. His mentor never showed that side to himself, only being there to urge Senku on. Even during the times that Senku managed to call Dr. X up in the middle of work and convince him to hide away in a bathroom stall, Senku was still the only one ever actually reaching an orgasm. Xeno... acted calm and collected the entire time. Turning the call off before touching himself. 

Senku's gaze moved down to look at his cock - still hard, it's form appearing in ripples beneath the calm water. His hand slowly reached down, grasping his full fist around it. Dr. X had taught him that, too. Before his mentor had taught him the proper way, Senku's masturbation sessions usually only included his thumb and forefinger. Realizing he could use his _entire_ hand? That was world changing.

Maybe... just _maybe_ , Dr. X was shy. Senku let his mind wander on that, hand slowly moving beneath the water, the movements causing the water to dance around him. Were Dr. X's moans loud? Maybe they were super girly and cute, and he didn't want his student to hear them and tease him about it. Senku tried to imagine it - envision what his mentor's voice would sound like, out of breath and panting, whispering his name into Senku's ears, telling him only _then_ how tight he actually was... 

It didn't take much effort or time at all before the small strings of white were floating through the water, Senku's grip still tight as his body shook and tensed with his orgasm. His afterglow could only last so long, his mind quickly focusing on how he had now dirtied the water. Even if it was his own body, Senku didn't like the idea of swimming inside his own mess, and soon lifted himself from the tub as soon as his post-orgasm fog had left him. 

Once dry, Senku saw the small notification on his phone that signaled a text message. The name above the message preview also showed that the message was from the very scientist that just totally tried to blue-ball him. With a sharp scoff, Senku wrapped the towel around his waist, opening the message, brows knitting with irritation as he quickly began to text his mentor back. 

Dr.❌  
  
So you DID have a show planned for me.  
  
Screw off, old man! I'm mad at you 😡  
  
You're very cute.  
  


* * *

Senku felt so damn _proud_ of himself. He was not usually one for boasting, but he didn't even need to. The grin that he was shooting up at Xeno was enough. He couldn't say no! The silly company barbecue would be at the nearby beach! Xeno would be an idiot to pass up the chance to see him in a bathing suit. Not to mention all the flack that Xeno would catch if he _did_ say no, to _his_ pleading face. He had planted those roots so carefully, so _easily_. He was Xeno's little junior apprentice, now. Across the room, other eyes had looked over, all waiting for Xeno to cave in. Everyone thought Xeno had a soft spot for him because of his bright mind!

If they only knew the truth!

Xeno's eyes began to close as he sighed. An action that only brought even more excitement to Senku's face. This was it! He had won!

"When is it?" Xeno asked then, his voice low and monotone, definitely not sharing Senku's excitement for all of this working. 

"Tomorrow," Byakuya said with a wide grin, Senku knowing that his dad also felt that air of success, "everyone is meeting down at the beach."

The mention of the beach only seemed to deter Xeno even more, but with a deep breath, he asked Byakuya which they would be attending. That enthusiasm (or lack thereof) lessened even more when Byakuya spoke the name of the beach - one very far from where most of the NASA workers commuted from. 

"It's a nice beach," Byakuya said with a nod, "it's out of the way, but that means it's less crowded."

Senku's grip tightened even more on Xeno's arm, a motion no one would be able to notice aside from the two of them. _Less crowded_ . That's a good thing. He had _yet_ to get this guy alone! Always playing hard to get!

"Hmm," Xeno seemed to be deep in consideration, but Senku knew there was no point. He wouldn't say no after asking the questions, and he wouldn't say no with Senku latched so lovingly to his arm! "My schedule for tomorrow is clear. I will... see if I can attend. You may email me the time and address." 

A laugh came from Byakuya, "Well! That's better than an outright 'no'. I'll make sure you get that email, then." His gaze now fell to Senku, an arm outstretched, "Come on, Senku. Don't bother poor Xeno _too_ much."

Senku did let go, his arms folding behind his back as he returned to his father. The conversation could have ended there, he had _won_ this battle, but as he walked away with Byakuya, Senku turned his head back to shoot one more grin back at his mentor, "you're not allowed to wear your lab coat down at the beach! You have to wear something light!" The look of pure disdain that Senku got back was entirely worth it, making his smirk grow even wider. 

Xeno was not as easy to control as Byakuya... but damn if the guy wasn't still easy!

* * *


End file.
